Disposable nappies generally consist of an absorbent filler protected on its outer face by a liquidproof polyethylene film and covered internally with a film of nonwoven fabric, generally of polyethylene, which comes into contact with the skin and allows body fluids to flow towards the said filler. More elaborate nappies may, in addition, contain a leakproof barrier of polyolefinic nature and/or an elastic waistband.
The nappies are conventionally prepared by adhesively bonding the various constituents with the aid of hot-melt adhesives whose composition can vary depending on the chemical nature of the components to be assembled. Such adhesives are described, for example, in the documents which follow.
U.S. Pat. No. 4,526,577 proposes an adhesive including a block copolymer A-B-A (in which A denotes a nonelastomeric block, for example styrene, and B denotes butadiene or hydrogenated butadiene), a compatible tackifying resin, a plasticizing oil and a stabilizer and, optionally, a wax originating from petroleum.
U.S. Pat. No. 4,460,728 describes an adhesive based on an ethylene-vinyl acetate or alkyl acrylate copolymer, on atactic polypropylene and on a compatible tackifying resin, optionally in the presence of a plasticizing oil and/or of a wax originating from petroleum and/or of a stabilizer.
U.S. Pat. No. 4,939,202 proposes a moisture-resistant adhesive containing a propylene-based amorphous polymer, a propylene-based crystalline polymer and a petroleum resin containing hydrocarbons containing from 4 to 10 carbon atoms.
U.S. Pat. No. 4,149,741 employs a hot-metal adhesive including a styrene-isoprene-styrene block copolymer, a compatible tackifying resin, a plasticizing oil and a stabilizer and, optionally, a wax derived from petroleum.
Catamenial liners, for their part, generally include an absorbent filler of the cellulose fluff or superabsorbent type and a covering based on a nonwoven fabric made of polypropylene or of viscose, to the outer face of which covering an adhesive composition is applied allowing positioning on the undergarment. To manufacture such liners the compositions described in the following documents have been proposed.
EP 0104005-A proposes an adhesive based on a viscoelastic elastomer of A-B-A type (in which B denotes a polyolefin, for example an ethylene-butylene copolymer and A includes a polystyrene), and on a tackifying resin.
Finally, in WO 93/10734 a composition is described including a copolymer of formula (A-B).sub.n -Y (in which Y is a multivalent coupling agent, A is a vinyl monomer substituted by an aromatic radical and B is polybutadiene), a compatible tackifying resin and a plasticizing oil.
The adhesives of the prior art which have just been mentioned are not entirely satisfactory in the field of hygiene.
Thus, in the case of disposable nappies, the polypropylene-based hot-melt adhesives (U.S. Pat. No. 4,460,728 and U.S. Pat. No. 4,939,202) are difficult to use in conventional devices operating by fiberizing or spraying, and the compositions described in U.S. Pat. No. 4,526,577 and U.S. Pat. No. 5,149,741 exhibit poor behaviour towards water, which can result in particular in the separation of the absorbent filler adjoining the leakproof film.
In the case of catamenial liners the abovementioned adhesive compositions are found to be satisfactory when applied to a covering made of nonwoven fabric. However, it is found that the said compositions are not suited for the preparation of latest-generation ultrafine liners which comprise a covering consisting of a polyethylene-based open-worked or perforated film. It is found, in fact, that the use of compositions based on ethylene-vinyl acetate copolymer results in soiling of the covering and that the adhesives according to EP 0 104 005-A and WO 93/10734 must be applied at an elevated temperature, of the order of 150 to 180.degree. C., in order to adhere to the support in a satisfactory manner.